Southern California Conferences for Undergraduate Research

Effects of Soil Temperature and Moisture on Stomatal Density and Water Use Efficiency in Pseudotsuga macrocarpa

Authors:

Daniel Mendes, Peter Pellitier

Mentor:

Frances Hanzawa, Professor of Biology, Pomona College

A consequence of climate change for plants is that the habitat in which they are growing may become warmer and drier than the species optimum for survival and growth. Our goals were to determine abiotic stresses being placed on a montane tree along an elevational gradient and to examine whether they are acclimatizing to their environment through morphological or physiological changes. In response to rising temperatures, many plant species have been found to produce fewer stomata in leaves in order to combat loss of water vapor through transpiration. Delta C 13 is a measure of the isotopic ratio of carbon 13 to carbon 12 in a sample material. Delta C 13 is a useful measurement of how plants are reacting to water deficit stresses because it has functions as an estimate of plants’ water use efficiency. Pseudotsuga macrocarpa is a conifer endemic to mountains in southern California. Individuals at the lower part of the P. macrocarpa elevational range could be under greater abiotic stress than trees at higher elevations due to hotter temperatures and less available water. We measured temperature and soil moisture at trees and the stomatal density and delta C 13 of year-old needles from those trees. We found that delta C 13 increased across elevation, indicating that trees at lower elevations have a higher water use efficiency, which suggests that they have acclimatized to a more intense water deficits. We also found that stomatal density decreased as soil temperature increased, suggesting that the trees at hotter sites are conserving water by reducing transpiration. Greater water stresses are being placed on trees at lower elevations, but there is evidence that they are acclimatizing. As climate continues to change, however, it may be difficult for the trees to acclimatize to more extreme conditions.